Impact tool



1 J. E. CONNOLLY 3535 910 IMPACT TOOL Filed March 11. 1966 I l l l 10 Il F! G. 2' 16 l I l l I l l l a l za -k 5 I f iii INVENTO/P JOHN 'E.CONNOLLY A TTORNEYS United States Patent 3,535,910 INIPACT TOOL John E.Connolly, Hamburg, Mich. (300 Lillian Court, Whitmore Lake, Mich. 48189)Filed Mar. 11, 1966, Ser. No. 533,504 Int. Cl. B211 13/06 US. Cl. 724799 Claims ABSTRACT OF THE DISCLOSURE This invention relates to an impacttool and to the method of forming the same. It is common in formation ofimpact tools to have a head larger than the shaft of the tool to reducethe impact load on the head to prevent deformation and still transmit anadequate axial impact to the tool shaft. There are many types of toolsto which the present invention is related, namely chisels, rock tools,metal punches, air hammer tools for concrete and rock, pin punches,punch-press punches, header punches, hot forging punches and the like.

It is an object of the present invention to provide an inexpensive meansfor forming a shock tool having ideal metallurgical characteristics inthe shaft or tool and with an inherent basic form with an enlarged headresulting from the general formation of the part in the heat treat ingprocess.

Reference is made to the US. patent to Schmatz et al., No. 2,934,463,issued Apr. 26, 1960, directed to a method of producing a high strengthsteel and the disclosure of that patent is incorporated herein for adetailed disclosure on the process of creating a tempered martensiticstructure.

This method involves a high degree of working on the metal itself toeffect a material deformation in the metal as a part of the process ofchanging the metallurgical characteristics thereof. Accordingly, thedisclosure of this patent is incorporated herein for the purpose ofexplaining the various metals that might be used and also the process offorming it. The compositions which are considered ideal for the shaftsof the impact tools are generally referred to as ultrafine, grainedmartensite, hereinafter referred to, for purposes of convenience, astempered martensite.

High speed steels have proven in practice to be very shock sensitive,that is, subject to thermal and mechanical fatigue resulting from aslight crack or crevice on the surface resulting from tool marks and thelike. In the present invention, it is intended that the tool be formedover highly polished dies without decarburization such that a finesurface is supplied to minimize the presence of these surface defects.In addition, high speed (.83 carbon tool steel) treated in the mannerdescribed in the Schmatz patent, above identified, not only showsextremely high strength common to high speed steels, but this isaccompanied by a ductility which has never been previously obtained inhigh speed steel. Tests have indicated that the life of parts thusformed is two to eight times that of parts which have beenconventionally heat treated.

The method of the Schmatz patent disclosure involves a high degree ofworking of the metal from the point of view of volume change. It is anobject of the present invention to use the characteristic of the formingprocess to produce a shape inherently desirable in the tools to be made.

Other objects and features of the invention relating to details ofconstruction and operation will be apparent in the following descriptionand claims.

Drawings accompany the disclosure and the various views thereof may bebriefly described as:

FIG. 1, a general outline of an impact tool.

FIG. 2, a view of an impact tool as conventionally mounted.

Referring to the drawings:

In FIG. 1, there is shown in dotted lines a slug of material 10 which isto be used to form the punch 12 having a head 14 and a work shaft 16.The slug 10 is preferably formed of a steel described in the Schmatzpatent and in the process of heat treating which requires considerabledeformation of the steel, the lower portion of the slug 10 is reduced indiameter and elongated to provide the shaft 16 which has the highstrength characteristics described in the Schmatz patent. Highlypolished die surfaces are used to provide a smooth part surface formedto within a few thousandths of an inch of final size. The upper portionof the final tool designated 14 continues to have a reasonably largearea compared to the small end to absorb and distribute the loads whichwill be transmitted by a hammer or a bed plate. The forming can beaccomplished without noticeable decarburization, thus contributing to aproper surface condition.

The tool is formed with a progressively decreasing diameter in arelatively smooth uniform curve so that there is a good distribution ofthe shock load to the punch with a uniform, low-concentrated, stresstransition area to face the input of the loading. The deformation of themetal in the heat treat process can vary from 25 percent on up, but itis preferred that it be in the area of percent to obtain best results.

In carrying out this invention, a suitable steel composition is firstaustenitized by heating to a suitable temperature and then quicklybrought into the selected temperature region by quenching in a liquidmaintained at the proper temperature which should fall within theselected temperature region. This temperature region lies between 600 F.and l' F. with a preferred range from 800 F.

to 1050 F. However, the preferred range may vary according tocomposition and fabrication techniques. Baths of molten lead or moltensalt will serve well for this purpose. When the steel composition hasbeen quenched to the proper temperature, it is promptly worked to effecta substantial reduction of area before it has cooled below the selectedtemperature region into a region in which rapid transformation tobainite or other austenite decomposition products is possible. If thework is very severe, precautions should be taken that the metal is notheated by the energy of the working so as to approach or trespass in thetemperature zone in which a transformation into pearlite is possible.

When the desired amount of deformation or work has been accomplished,the steel composition is quenched into the martensite transformationzone before any transformation of substance into austenite decompositionproducts takes place. This quench is into the martensite transformationzone and is sufficiently drastic to insure a predominantly martensiticmicrostructure. In most circumstances an ordinary water quench isadequate for this purpose.

The martensitic structure obtained by this quenching procedure must betempered to obtain the optimum final results. Tempering may beaccomplished at any temperature desired in the range of F. to 750 F.depending upon the final properties desired. A progressive increasetakes place in the ratio of yield strength to tensile strength as thetempering temperature increases. This ratio is about 0.71 at 150 andincreases to 0.93 at 600 F. The preferred tempering range is 350 F. to700 F.

In the practice of this invention, it is preferred to rely upon chromiumor nickel and chromium to stabilize the austenite against prematuredecomposition. However it is to be understood that other elements knownto have the same effect may also be so employed. Examples of suchelements are boron, manganese and nitrogen.

To insure an adequate bay width between the pearlite transformation zoneand the bainite transformation zone, additions of molybdenum may bemade. A similar effect may also be had by additions of manganese,vanadium and tungsten.

Thus it will be seen that the high strength areas of the punch areproduced in a small diameter in the shaft 12 as a result of the heattreating operation leaving a part which is inherently of the properdiameter and shape to serve as an impact tool with an enlarged head 14and a work shaft 16. This produces a part immediately adaptable tomounting in a conventional structure such as shown in FIG. 2 wherein animpact plate 16 has the impact tool 12 mounted by its head 14 retainedby a plate 18 having a suitable opening 20 for surrounding the head 14and holding it tightly to the base plate 16. In most instances, the toolcan be formed in the heat treating process and the deformation requiredthereby to within a few thousandths of an inch of the finished size. Ifnecessary some finished grinding can be used to size the part but nomachining is necessary and thus surface cuts and abrasions can beavoided.

The resulting tool can receive loads as high as 400,000 pounds persquare inch and has a ductility as high as 10 percent with no bittlecharacteristics.

Thus, by utilizing the method of creating the best known metalcharacteristic for the punch itself, the shape desired is also obtainedas well as proper surface condition for an ideal punch construction.

The small diameter of the tool formed in the dastic working of the metalat the temperature range of 750 to 1050 F. gives the so-called ausformstrength and high ductility providing resistance to fracture and fatiguein the area where the high loads are present. The large diameter willremain with substantially normal characteristics where there is lowerp.s.i. load.

In one example with a 60 percent reduction using H-13 tool steel, thehardness has varied from 59.5 to 61 (Rockwell Scale) in the small shankarea and ranges down to 54 in the head area. The expected life of thetool can be extended three to five times that of normal tool steel heattreated in a conventional way.

What is claimed as new is as follows:

1. The method of making a steel punch of the type having a working shaftportion of elongate form of a predetermined cross-section and anenlarged mounting and driving head of substantially larger cross-sectionthan the shaft which comprises:

(a) selecting a cylindrical slug of tool steel having a diametersubstantially equal to the intended final diameter of the head of thepunch,

(b) heating the slug to a temperature to obtain an austenitic grainstructure,

(c) quenching the slug from a temperature range at which austenite isstable into a selected temperature region below the temperature at whichaustenite transforms into pearlite and drastically working one end ofthe slug within said temperature range to decrease its cross-section tothe desired cross-section of the working shaft portion while maintainingthe austenitic grain structure and while maintaining the basiccross-sectional dimension of the mounting head,

((1) quenching the formed punch from said temperature range to obtain apredominantly fine-grained martensitic structure in the worked end, and

(e) tempering the punch to obtain a high tensile and yield strengthcharacteristic in the ensmalled end.

2. The method of making a steel punch of the type having a working shaftportion of elongate form of a predetermined cross-section and anenlarged mounting and driving head of substantially larger cross-sectionthan the shaft which comprises:

(a) selecting a cylindrical slug of tool steel having a diametersubstantially equal to the intended final diameter of the head of thepunch,

(b) heating the slug to a temperature to obtain an austenitic grainstructure,

(c) quenching the slug from a temperature range at which austenite isstable into a selected temperature region below the temperature at whichaustenite transforms into pearlite and drastically working one end ofthe slug within said temperature range to decrease its cross-section tothe desired cross-section of the working shaft portion and to form atransitional portion between said shaft and said head of graduallyincreasing cross-section while maintaining the austenitic grainstructure and while maintaining the basic cross-sectional dimension ofthe mounting head,

(d) quenching the formed punch from said temperature range to obtain apredominantly fine-grained martensitic structure in the worked end, and

(e) tempering the punch to obtain a high tensile and yield strengthcharacteristic in the ensmalled end.

3. A steel impact tool comprising a working shaft portion of elongateform of a predetermined diameter, an enlarged mounting head portion ofapproximately twice the diameter of the shaft, and a blending portionbetween said shaft and head portions curving gradually from the shaftportion to the head portion, the shaft of said tool being formed by theprocess of creating tempered martensite which comprises heating acylindrical slug of steel to a temperature sufficient to render thestructure of the steel austenitic, the chemical composition of saidsteel slug being such that it exhibits a metastable austenite structureunder conditions of substantial working when quenched from a temperatureat which austenite is stable into a selected temperature region belowthe temperature at which austenite transforms into pearlite and abovethe temperature at which austenite transforms into bainite within thetime necessary for the working process, quenching the entire slug as anaustenitic mass sufliciently drastically to avoid any transformationinto pearlite and to bring the slug to the selected temperature regionwithout permitting any substantial transformation into bainite,performing a substantial amount of work upon one end of the steel slugwhile maintaining the temperature of the slug within the selectedregion, said work being sufficient to effect a substantial reduction incross-sectional diameter at said one end to form a working shaft,quenching the steel slug from the selected temperature region to atemperature at which the isothermal transformation products will bepredominantly martensitic and tempering the martensitic structure soobtained to increase the yield point and to narrow the range between theyield point and the tensile strength whereby a fine grained martensiticproduct is obtained in the reduced end of the slug in which themartensitic grain size is substantially smaller than the martensiticgrain size of the remainder of the slug which is transformed directly tomartensite without working of the metastable austenite, the resultingpiece being thereby dimensioned for use as an impact tool with amounting and drive portion at the large end and a working portion at thesmall end.

4. An impact tool of the type having a work shaft portion of reduceddiameter and a head portion of large diameter connected by a curvedblending area, said tool being formed without machining from a piece ofhigh speed steel, the shaft being subjected to a forming process tocreate the reduced diameter and simultaneously produce a highly ductilemetal of the nature of tempered martensite by a process which comprisesheating a selected steel slug to a temperature sufiicient to render thestructure of the steel austenitic, the chemical composition of saidsteel slug being such that it exhibits a metastable austenite structureunder conditions of substantial working when quenched from a temperatureat which austenite is stable into a selected temperature region belowthe temperature at which austenite transforms into pearlite and abovethe temperature at which austenite transforms into bainite within thetime necsssary for the working process, quenching the entire slug as anaustenitic mass sufficiently drastically to avoid any transformationinto pearlite and to bring the mass to the selected temperature regionwithout permitting any substantial transformation into bainite,performing a substantial amount of work upon one end of the steel slugwhile maintaining the temperature of the slug within the selectedregion, said work being sufficient to effect a deformation of at leasttwenty-five percent at one end to form a working shaft, quenching thesteel slug from the selected temperature region to a temperature atwhich the isothermal transformation products will be predominantlymartensitic and tempering the martensitic structure so obtained in theensmalled end to increase the yield point and to narrow the rangebetween the yield point and the tensile strength whereby a fine grainedmartensitic product is obtained in the reduced end of the slug in whichthe martensitic grain size is substantially smaller than the martensiticgrain size of the remainder of the slug which is transformed directly tomartensite without working of the metastable austenite, the resultingpiece being thereby dimensioned for use as an impact tool with amounting and drive portion at the large end and a working portion at thesmall end.

5. An impact tool of the type having a work shaft portion of reduceddiameter and a head portion of large diameter connected by a curvedblending area, said tool being formed without machining from a piece ofhigh speed steel, the shaft being subjected to a forming process tocreate the reduced diameter and simultaneously produce a highly ductilemetal of the nature of tempered martensite by a process which comprisesheating a selected steel slug to a temperature sufficient to render thestructure of the steel austenitic, the chemical composition of the steelslug including sufiicient chromium that it exhibits a metastableaustenitic structure under conditions of substantial working whenquenched from a temperature at which austenite is stable into a selectedtemperature region below the temperature at which austenite transformsinto pearlite and above the temperature at which austenite transformsinto pearlite and above the temperature at which austenite transformsinto bainite within the time necessary for the working process,quenching the entire slug as an austenitic mass sufficiently drasticallyto avoid any transformation into pearlite and to being the mass to theselected temperature region without permitting any substantialtransformation into bainite, performing a substantial amount of workupon the one end of the steel slug while maintaining the temperature ofthe slug within the selected region, said work being sufficient toeffect a deformation of at least twenty-five percent at one end to forma working shaft, quenching the steel slug from the selected temperatureregion to a temperature at which the isothermal transformation productswill be predominantly martensitic and tempering the martensiticstructure so obtained in the ensmalled end to increase the yield pointand to narrow the range between the yield point and the tensile strengthwhereby a fine grained martensitic product is obtained in the reducedend of the slug in which the martensitic grain size is substantiallysmaller than the martensitic grain size of the remainder of the slugwhich is transformed directly to martensite without working of themetastable austenite, the resulting piece being thereby dimensioned foruse as an impact tool with a mounting and drive portion at the large endand a working portion at the small end.

6. An impact tool of the type having a work shaft portion of reduceddiameter and a head portion of large diameter connected by a curvedblending area, said tool being formed without machining from a piece ofhigh speed steel, the shaft being subjected to a forming process tocreate the reduced diameter and simultaneously produce a highly ductilemetal of the nature of tempered martensite by a process which comprisesheating a selected steel slug to a temperature suflicient to render thestructure of the steel austenitic, the chemical composition of saidsteel slug being such that it exhibits a metastable austenitic structureunder conditions of substantial working when quenched from a temperatureat which austenite is stable into a selected temperature region belowthe temperature at which austenite transforms into pearlite and abovethe temperature at which austenite transforms into bainite within thetime necessary for the working process, said selected temperature regionextending from six hundred degrees Fahrenheit to one thousand onehundred degrees Fahrenheit, quenching the entire slug as an austeniticmass sufiiciently drastically to avoid any transformation into pearliteand to bring the mass to the selected temperature region withoutpermitting any substantial transformation into bainite, performingsufiicient work upon the one end of the steel slug while maintaining thetemperature of the slug within the selected region to reduce thecross-section and deform the said one end at least ninety percent,quenching the steel slug from the selected temperature region to atemperature at which the isothermal transformation products will bepredominantly martensitic and tempering the martensitic structure soobtained in said reduced end to increase the yield point and to narrowthe range between the yield point and the tensile strength whereby afine grained martensitic product is obtained in the reduced end of theslug in which the martensitic grain size is substantially smaller thanthe martensitic grain size of the remainder of the slug which istransformed directly to martensite without working of metastableaustenite, the resulting piece being thereby dimensioned for use as animpact tool with a mounting and drive portion at the large end and aworking portion at the small end.

7. An impact tool of the type having a work shaft portion of reduceddiameter and a head portion of large diameter connected by a curvedblending area, said tool being formed without machining from a piece ahigh speed steel, the shaft being subjected to a forming process tocreate the reduced diameter and simultaneously produce a highly ductilemetal of the nature of tempered martensite by a process which comprisesheating a selected steel slug to a temperature sufficient to render thestructure of the steel austenitic, the chemical composition of the steelincluding sufficient chromium that it exhibits a metastable austeniticstructure under conditions of substantial working when quenched from atemperature at which austenite is stable into a selected temperatureregion below the temperature at which austenite transforms into pearliteand above the temperature at which austenite transforms into bainitewithin the time necessary for the working process, said selectedtemperature region extending from six hundred degrees Fahrenheit to onethousand one hundred degrees Fahrenheit, quenching the entire slug as anaustenitic mass sufficiently drastically to avoid any transformationinto pearlite and to bring the mass to the selected temperature regionwithout permitting any substantial transformation into bainite,performing a substantial amount of work upon one end of the steel slugwhile maintaining the temperature of the slug within the selectedregion, said work being sufficient to effect a deformation of at leasttwenty-five percent at one end to form a working shaft reduced incross-section from that of the original slug, quenching the steel slugfrom the selected temperature region to a temperature at which theisothermal transformation products will be predominantly martensitic andtempering the martensitic structure so obtained in the reduced end toincrease the yield point and to narrow the range between the yield pointand the tensile strength whereby a fine grained martensitic product isobtained in the reduced end of the slug in which the martensitic grainsize is substantially smaller than the martensitic grain size of thesame steel in the remainder of the slug which is transformed directly tomartensite without working of the metastable austenite, the resultingpiece being thereby dimensioned for use as an impact tool with amounting and drive portion at the large end and a working portion at thesmall end.

8. An impact tool of the type having a work shaft portion of reducedcross-section and a head portion of large cross-section connected by acurved blending area, said tool being formed without machining from apiece of high speed steel, the shaft being subjected to a formingprocess to create the reduced diameter and simultaneously produce ahighly ductile metal of the nature of tempered martensite by a processwhich comprises selecting a slug having a steel composition exhibiting ametastable austenitic structure under conditions of working whenquenched from a temperature at which austenite is stable into a selectedtemperature region below the temperature at which austenite transformsinto pearlite and above the temperature at which austenite transformsinto bainite within the time necessary for the working process, heattingthe steel slug to render it stably austenitic, quenching theaustenitized hardenable alloy steel composition sufficiently drasticallyto avoid any transformation into pearlite and to bring the compositionto the selected temperature region, performing a substantial amount ofwork upon one end of the steel slug while maintaining it in saidselected temperature region until the substantial amount of work hasbeen completed to reduce the crosssection of said one end, said workbeing sufiicient to effeet a deformation of said end to at leasttwenty-five percent, quenching the entire slug from the selectedtemperature region to a temperature at which the transformation productsWill consist essentially of martensite, said quenching operation beingsufficiently drastic to insure a structure consisting essentially ofmartensite, and tempering the martensitic structure so obtained in saidreduced end to narrow the range between the yield point and the tensilestrength and to enhance the ductility, whereby a product is obtained inwhich the martensitic grain size in said one end is not over one-half ofthe martensitic grain size of the head end of the slug which istransformed directly to martensite without working of the metastableaustenite, the resulting piece being thereby dimensioned for use as animpact tool with a mounting and drive portion at the large end and aworking portion at the small end.

9. An impact tool of the type having a work shaft portion of reduceddiameter and a head portion of large diameter connected by a curvedblending area, said tool being formed without machining from a piece ofhigh speed steel, the shaft being subjected to a forming process tocreate the reduced diameter and simultaneously produce a highly ductilemetal of the nature of tempered martensite by a process which comprisesselecting a slug having a steel composition exhibiting a metastableaustenitic structure under conditions of working when quenched from atemperature at which austenite is stable into a selected temperatureregion below the temperature at which austenite transforms into pearliteand above the temperature at which austenite transforms into bainitewithin the time necessary for the working process, heating the slug torender it stably austenitic, quenching the austenitized hardenable alloysteel composition sufficiently drastically to avoid any transformationinto pearlite and to bring the composition to the selected temperatureregion, performing a substantial amount of work upon one end of the slugto reduce the cross-section while maintaining it in said selectedtemperature region until the substantial amount of work has beencompleted, said work being sufiicient to effect a deformation of saidend of at least ninety percent, quenching the entire slug from theselected temperature region to a temperature at which the transformationproducts will consist essentially of martensite, said quenchingoperation being sufiiciently drastic to insure a structure consistingessentially of martensite, and tempering the martensitic structure soobtained, the resulting piece being thereby dimensioned for use as animpact tool with a mounting and drive portion at the large end and aworking portion at the small end.

References Cited UNITED STATES PATENTS 254,195 2/1882 Brown 724792,934,463 4/1960 Schmatz et a] l4812.4

RICHARD J. HERBST, Primary Examiner US. Cl. X.R. 148--l2.4

